External minecraft renderers can't easily grab the biome color data from the NBT data, so they need to be given that data somehow

Having the option for terra to export that data to a file would be very useful

preferably in the syntax:
minecraft:plains = #91bd59, #77ab2f, #3F76E4
with the colors (in order) being for grass, foliage and water

Minecraft has more than just the colors you listed (for example fog) if we were to export in that format we'd also include all other colors

If this is being implemented, I'd suggest using a standard and exporting it in the format of a normal minecraft datapack. Even if this doesn't result in a complete and functional minecraft-datapack it would be compatible with everything that can load biome-info from a datapack.
BlueMap for example can already use a datapack to figure out all the biome-colors :)

@TBlueF can you link to documentation on what BlueMap is reading from a data pack?

BlueMap is reading those biome files https://minecraft.fandom.com/wiki/Custom_biome from a datapack
and is effectively using the downfall, temperature, effects.water_color, effects.foliage_color and effects.grass_color values

https://github.com/repository/terra-biome-colors-parser